Forward-masked psychophysical spatial tuning curves (fmSTCs) were measured in twelve cochlear-implant subjects, six using bipolar stimulation (Nucleus devices) and six using monopolar stimulation (Clarion devices). fmSTCs were measured at several probe levels on a middle electrode using a fixed-level probe stimulus and variable-level maskers. The average fmSTC slopes obtained in subjects using bipolar stimulation (3.7 dBmm) were approximately three times steeper than average slopes obtained in subjects using monopolar stimulation (1.2 dBmm). Average spatial bandwidths were about half as wide for subjects with bipolar stimulation (2.6 mm) than for subjects with monopolar stimulation (4.6 mm). None of the tuning curve characteristics changed significantly with probe level. fmSTCs replotted in terms of acoustic frequency, using Greenwood's [J. Acoust. Soc. Am. 33, 1344-1356 (1961)] frequency-to-place equation, were compared with forward-masked psychophysical tuning curves obtained previously from normal-hearing and hearing-impaired acoustic listeners. The average tuning characteristics of fmSTCs in electric hearing were similar to the broad tuning observed in normal-hearing and hearing-impaired acoustic listeners at high stimulus levels. This suggests that spatial tuning is not the primary factor limiting speech perception in many cochlear implant users.
|Original language||English (US)|
|Number of pages||22|
|Journal||Journal of the Acoustical Society of America|
|State||Published - 2008|
Bibliographical noteFunding Information:
This work was supported by NIDCD Grant No. R01-DC006699 and by the Lions 5M International Hearing Foundation. John Van Essen converted Robert Shannon’s computer software into the C language and made modifications to that software for testing Nucleus subjects. Cochlear Corporation provided Nucleus subjects’ calibration tables. Advanced Bionics Corporation provided the research interface used for testing Clarion subjects, and Eric Javel developed the experimental software to control that interface. The authors would like to extend special thanks to the subjects who participated in this work, and to Andrew Oxenham, Bob Shannon, and an anonymous reviewer, who made valuable suggestions during the review of this manuscript. 1